Method of recovering tin from tin-bearing materials



Patented Oct. 9, 1951 METHOD OF RECOVERING TIN FROM TIN-BEARING MATERIALS Irving E. Muskat and Robert H. Taylor, Plainfield, N. J., assignors to The Vulcan 'Detinnmg Company, a corporation of New Jersey No Drawing. Application.May 17., 1946, serial No. 670,547

3 Claims. (Cl. 23-136) This invention, is directed to. the recovery of tinfrom tin ores and other tin-bearing materials by an improved process involving the sulfidizing of. the tin content and the volatilization of the resulting tin sulfide, which can be collected-andtreated to recover the tin by known methods.

It isknown to recover tin from tin-bearing materials such as ore by the conversion of the tin content of the material undergoing treat,- ment to a sulfide and the. subsequent vol'atization of'the resulting tinsulfide. :It is also known that better yields of tin are obtained in accordance with such processes if the sulfidizing reaction is carried out in the presence of a reducing agent. In one such process the tin ore is heated to a reducing temperature below the fusion temperature and at that time there is brought in contact with the heated ore a liquid or solid reducing agent and a non-gaseous sulfidizing agent to.

effect the conversion and volatinzationof .tin sulfide. In another such process'the tin ore is heated in the presence of a reducing agent and a sulfur compound to a temperature at which reduction occurs, and the heating of the mixture is .continued until conversionofthetin and volatilization of the resulting: tin sulfideis efiected.

Insofar as. we are-aware, noneof these prior art .tin ore sulfidizingcprocesses has met with commercial success because fusion of the ore took place with consequent. substantial impairment of the yields of recoverable tin, atthesunidizing and volatilization temperatures of about 950C. to 'l100 C. Moreover, thetime required to effect sulfidization and volatilization of tin sulfide from the ore in accordance with these prior art processes was so inordinately long as to make-their use commercially unfeasible.

We havefound that if the tin ore is preliminarily reduced and if this reduction is carried out to an extent sufiicient to make the. reduced tin soluble in an aqueous alkali metal hydroxide solution at a temperature of at least about 75: C. to 90 C., that whenv this reduced ore is sulfidized at. temperatures. of about 950 C. to-1'100 GQto volatilize thet-in from the ore as tin sulfide no fusion or no substantial fusion of the ore takes place. In consequence there is a. greater yield of recoverable than in the prior :art processes referred to above. Additionally, these greater yields of recoverable tin are obtained in considerably less time than heretofore. For ex ample, we hav'e obtained approximately 95 of.

the tin content .of'a Bolivian ore containingabout 22% of tin in'the form of tin sulfide by reacting, this ore in a reduced state in accordance with our invention with sulfur at sulfidiz'ing and volatilizing temperatures of about 1100 C., for

approximately one-quarter, to one-half hour.

Similar yields were obtained at lower sulfid-izing and volatilizing temperatures'of about. 1020 "G.;.

to 1060 C., in times varying from aboutone-hal-fto one hour.

In carryinggoutthe present invention with a tin ore'as thestarting materia-Lthe tin ore, either high grade: or low grade and concentrated -:'or

unconcentra'ted, either with or without prelimi-- nary roasting to remove sulfur, is subjected tocontrolled reducing conditionsso as to convert the tin content of the ore into a state in which most if not all of the tin is soluble in an aqueousalkali metal hydroxide solution, at a temperature in the orderof, at least about 7b" C. to 9U C..and

up to the boilmgpoint of thesoluti'on; By soluble it is meant that tne tin is in a form in which it may be converted to a Water Soluble stannate by reaction with an aqueous alkalimetal hydroxide,

of a concentrationof about 15%, and, of course,

higher, preferably in the presence of an oxidiz-- ing agent capable of oxidizing metallic tinin an. alkaline medium, at. the aforesaid temperature.

For substantially all. tin ores, including the lowgrade tin ores of .5 to 35% 'tin content, the reduc:-' tion is suiilciently complete in accordance with the present invention the tin content is soluble in an aqueous alkali metal hydroxide solus tion which contains. I3'0:gms..Na'OI-I and 40 gms. NaNOs per liter of solution, at a temperature of about C. Equivalent amounts of other alkali After the ore has been reduced to the a'foresaid state it is reacted with a sulfur-containing material at temperatures sufficiently high. to effect 'sulfidization of the reduced tin and. volatilization of the resulting tin sulfide. The. sulfidi'zr ing reaction maybe carried out in any suitable, vesselsuch as adirect-fired rotary kiln, for example, either in a-neutra'l atmosphere or a re.- ducing atmosphere, preferably the latter.- I dizing atmospheres should be avoided because such atmospheres induce ox'idizationof the tin.

and other'met'als intheore and thereby cut down.

3 the yields of recoverable tin and add to the cost of the process.

Where the tin content of the reduced ore is high, say in the order of about 35 l0% and higher, it is preferred to eifect the sulfidization of the reduced ore in the presence of a solid carbonaceous reducing agent, such as coal in a powdered state, in substantially uniform admixture with the reduced ore. carbonaceous reducing agent. is a safeguard against fusion of the reduced ores at the sulfidizing and volatilizing temperatures of up to about 1100 C. The amount of solid carbonaceous reducing agent which may be added to the reduced ore to prevent fusion may vary rather widely, as desired, from about 5% to 40%, based on the weight of the ore.

Any sulfur-containing material, solid, liquid or gas, capable of reacting with tin at a temperature of from about 950 C. to 1100 C. to form a tin sulfide may be used in accordance with the present invention. The amount of sulfidizing agent which may be used may vary widely, from about to 100% or even more, based on the weight of' the tin-containing material being treated, in the case of sulfur. Equivalent amounts of other sulfur-containing materials such as ferrous sulfide, sulfur dioxide sulfurcontaining petroleum-crudes, etc., may be used. Sulfur, however, is preferred because more of the tin is sulfidizedand in less time than with the other sulfidizing agents. Optimum results are usually obtained with a low grade reduced tin ore containing from about to35% of tin by using from about to 50% of sulfur, based on the weight of the ore.

4 The temperature at which the reduced tin ore is sulfidized and the tin volatilized therefrom in the form of a tin sulfide may vary from about 950 C. to 1100 C., the preferred temperatures varying fromabout'l020 C. to 1100. C. The time of treatment of the ore with a sulfidizing agent at these temperatures 'may vary widely, from about 15 minutes upwardlyJ Usually the maximum amount of tin is volatilized in the form of tin'sulfide' in about 15 minutes to one-half hour, although at times it is'essential to prolong the reaction'to about onehour in order'tovolatilize'the maximum amount of tin outof the ore; particularly at lower sulfidizing and volatilizing temperatures in the order of about 950 C. to 1050" C. Generally; sulfidizing reaction times in. excess of about one hour are ineffective to increase toany substantial extent the amount of tin which can be. volatilized from the ore in the form of, tin sulfide in. accordance with our process.

m the practice of the process herein contemplated to effect reduction, a tin ore in a finely divided state is heated in the presence of a quantity of a solid carbonaceous reducing agent capable of reducing tin oxide to metallic tin, such as carbon, coal, lampblack, petroleum coke, etc. for a time required and at a predetermined temperature to convert the tin content of the ore into the aforesaid soluble state. The ore treated may contain from about 5% to 60% and even more of tin, including both high grade and low grade ores, although for economic reasons it is preferred to treat a low grade tin concentrated or unconcentrated ore containing from about 15% to 35% or less of tin.

The reduction treatment of the ore is effected by heating the ore in a pulverized state, for example, minus 100 or 200 mesh, in the presence This added solid of a solid carbonaceous reducing agent such as coal, charcoal, carbon and coke, preferably in powdered form and preferably of a mesh corresponding substantially to the mesh of the ore. These solid carbonaceous reducing agents are preferredbecause they are :easier to handle and because they have the property of minimizing fusion and sintering of the ore. Solid carbonaceous materials containing both nonvolatile and volatile carbonaceous reducing agents, such as anthracite or bituminous coal, are most suitable for this purpose. Bituminous coal is preferred because of its relative cheapness and availability.

The reduction treatment should be conducted at a temperature sufiiciently high to permit a major part or all of the tin content of the ore to be converted to the aforesaid aqueous alkali soluble state; however, the temperature should not be so high that substantial fusion occurs and a molten pool of ore, slag or metallic tin or other molten material'is formed. A ball mill or other suitable grinding device may be employed to grind the ore to the'desired finely divided state. The ore may be ground to minus20 or 60 mesh, but better yields of reactable tinare obtained if the ore-is ball-milled-to the mesh above stated;

The exacttemperature which may be utilizedin the reducing-treatment is dependent largely upon the nature of the ore subjected to reduc tion. Thus, someBolivian ores fuse or melt to a very serious extent at a temperature. ofv about 870 C. On the other hand, other Bolivian ores and many Mexican ores may be subjected to temperatures as high as, about 980 C, or 1040 0.. without encountering serious fusion. Slight amounts of fusion resulting in some sintering of the ore undergoing treatment may be tolerated in most cases. On the other hand, fusion to an extent such that pools of molten material are formed is detrimental and should be avoided. In generaL'satisfactory results are usually obtained Within a temperature range of about 760 C(or' 815 C. to about 1100 (land for most tin ores a temperature'of from about 870 C. to"1040 C. is most effective. 'A preferred temperature range is from about 900C. to 1000 C. The period of time over which the ore is subjected to the reducing treatment is capable of considerable-variation, being largely dependent uponthe activity of the ore undergoing treatment. and the temperature .oftreatment. Generally speaking, the time required is shorter Where the temperature is high than where a lowertemperature is used. In an y case, however, ,unduly pro:-. longed heat treatment of the ore, is detrimental and should be avoided. v The actual optimum time, at the reduction temperature is usually quite short and usually does not exceed about 30 to 40 minutes for low-grade ores. Fromdata obtained by carrying out experiments in' a" reduction furnace, it appears that low-grade ores may be' reduced to a good product in a matter of from about 8 to 12 minutes and 'even less. These figures include the time required to heat the ore up tothe reduction temperature; which in typicalinsta-nces was shown to bethe order of I about 3 to 5 minutes. The reduction may be elf-- fectedin any suitable furnace, such as a hearth type furnace, for example, a multiple hearth,. Wedge type furnace, or a rotary furnace. j

The amount of reducing agent utilizedis, in eneral, dependent upon the temperature of treatment andthe type of furnace in which redliction'is effected. It has been observed that e e ate fromabout to 35 per cent ofltin,.notlesstham about. two times. theamount of carbon orgcoal; required} to reduce tin to the, metallicstate and; form carbon monoxide is preferred; Wherrthis; reduction. is. conductedin a. continuous. manner by useof a rotary kiln or.a. multiple hearth furriace or other similar. device, not less thamabouti 1'5 1t'o.20.- per cent by weight of carbonorlcoal; basedluponv the weight of the. ore, is used... for. mostcases, since with these amounts of solid? carbonaceous material, the tendency of the. ore;

t5 fuse andsinter at the temperatureofreduc-A tionijis, greatly lessened. In general, coal in excessj'of about 30per cent by weight is und'esirar to preventreoxidation of. the tin. The" cooled reduced: oretis' thereaftergsulfidized. This cooling treatment is not essenti'alfor the heated reduced ore may be treatedwith a-sulfidizing agent, particularly a sulfidizing agent in a gaseous state, normal or otherwise, inaccordance withthe present invention.

The reduced ore after the cooling treatment usually is in the form of a black or dark colored pulverulent or granular mass; containing tin 'in dispersed small particles in a form-'solubleinthe aforesaid" aqueous alkali solutions. Sometimes the mass may be more or less-clinkered or caked and may require a pulverizing or grinding treatment; say to minus 100 or'200- mesh, prior to the sulfidizing treatment at' temperatures of from about 950 C. to 1100 C. In the preferred operation, the reduced ore prior to the sulfidizing treatment should be in a finely divided state such as set forth above.

The exact nature of the reducting reactions is not known, although it is possible that the tin is reduced to a finely divided metallic state, the particles being separated by the excess coal and by other materials in the reduced ore. event, this reduced ore is more amenable to reaction with a sulfidizing agent, particularly sulfur, than is ore not similarly treated.

The following example is illustrative of a preferred embodiment of the present invention.

The ore preparatory to the sulfidizing treatment was roasted and reduced as follows:

Ore containing about 21% tin, 22% iron, 19% silica, 2% sulfur, and other impurities in minor amounts was roasted in an oil-fired rotary furnace in an oxidizing atmosphere at a temperature of about 815 C. The roasted ore, which contained about 0.7% sulfur, was ball-milled to a particle size passing a 100-mesh screen. 100 parts by weight of the milled ore was intimately mixed with parts of powered bituminous coal. The mixture was fed into an oil-fired rotary furnace maintained at a maximum temperature of about 980 C. and operated with a reducing atmosphere. The ore-coal mixture was fed in at a rate such that it passed through the furnace in about 15 minutes. The reduced ore was cooled In any in arnoiieoxidizingp atmosphere andthen.- b811-1- milled-rte;passea.-l0.0-mesh;=screen. j Approximately 2.0u-partsby.. weight of the reduced ball-milled ore were intimately mixedgwith IO-parts by weight. of; powdered sulfur and the mixture. was placed. in avessel. and .the. latten heated-for 30 minutes atatemperature oil-100? C., in. a. noneoxidizing atmosphere of.v nitrogen... Under ,these! conditions approximately v95 .of the, tincontentof'theore was volatilizedin the form. of tin. sulfide.

' a.similar.experimentwith the same reduced;

tin oreesul'fur, charge ,at a temperature of, 106d? (3.1, for 30 minutes... approximately 9,,f1%/Of the tin.

contentwas volatilized f'r'omthe ore. In another similar experiment with the same reducedltinore, using, 20. parts by; weight of the.or e,. 5'. parts by weight'fof powdered sulfur and a temperature of. 1050 C; for one hour, approximately 95%. of the, tin content was. volatilized' from the ore.

, Ithis manife'st.thatthe, details as .to time andjf temperature of reduction oflthetin ore andti'me and temperatureof sulfi'di'zationof the. reduced; ore. may bevaried',- asv may. also the proportions of coal to oreinthereduction. treatment and 'sulfur. to reduced. ore in the sulfidizing treatment', allas. hereinabove setforth. It'isalso manifest thatother sulfidizin'ggagents. such as ferrous suT- fide, etc. may be. used, although not'with the espje-i cially.desirableflresults obtainedwith sulfur.

Although'the invention has particular value forthe treatment of. tin ores; including tin ore; concentrates and? naturally." occurring minerals. containing tin, it may also beapplied' to the recovery of tin fromother tin-containingmaterials su'ch'as. tin-containing dressing" plant tailings' or. the spent tin ore residues'from other tin recovery processes. Thus,,forexample, it may be applied? to, the spent residues from the aqueous alkali leaching process of' re'covering tin' from reduced tin ores which is described and'claimed in the-co pending application to one of us, Serial No. 6154,825, filed-September 6; 1945, now Patent N01.

Inaccordanc'e with the processof the appliedtion to one of us', tin ore is reduced to such an extent that the tin content is soluble in an aqueous alkali metal hydroxide solution as herein described. The reduced tin ore is then treated with an aqueous alkali metal hydroxide to form an alkali metal stannate which is leached from the ore. The residues from that process are the spent residues hereinabove referred to. These spent residues are tin-containing materials in a. reduced state in accordance with the present invention. They contain varying amounts of tin, from about 1% to 8%.

These spent residues may be mixed with a sulfidizing agent with additional reduction and sulfidized in accordance with the present invention, either with or without the presence of a solid carbonaceous reducing agent. Thus, for example, when 20 parts of a ball-milled spent residue containing 2.4% tin from the alkali process of the aforesaid application were mixed with 10 parts of powdered sulfur and sulfidized at 1060 C. for 30 minutes as herein described, approximately 87% of the tin content was volatilized in the form of tin sulfide. With the same spent residue and 12 parts of powdered sulfur and 4 parts of powdered coal, using again a temperature of 1060 C. for 30 minutes, approximately 90% of, the tin content was volatilized in the form of tin sulfide.

The recovery of the tin from the tin sulfide forms no part of our invention. Any of the conventional methods may be used for this purpose;

such as those referred to in the British Patent No. 361,402, accepted November 18, 1931, for example.

In our copending application Serial No. 670,548,

filed on even date herewith, there is disclosed and claimed a process of recovering tin in the form about 15% to 35% of tin in a form in which it' is in a substantially aqueous alkali-insoluble state, comprising heating such ore in the'presence of about to 40% of a solid carbonaceous reducing agent, based on the weight of the ore, at a temperature of at least about 760 C. but below that at which the ore fuses, under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solu=- tion at a temperature of at least about 75 C. to

90 C. is produced, and heating the product of such treatment containing the said soluble tin with a sulfidizing agent at a temperature of about 950 C. to 1100 C. to form tin sulfide and for a time suflicient to volatilize thesame from the ore undergoing treatment.

' 2. A process for recovering tin in the form of tin sulfide from a low grade tin ore containing about 15% to 35% of tin in a form in which it is in a substantially aqueous alkali-insoluble state,

comprising heatin such ore in the presence of about 5% to 40% of a solid carbonaceous reducing agent, based on the weight of the ore, at a temperature of at least about 760 C. but below that at which the ore fuses, under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution at a temperature of at least about 75 C. to 90C. is produced, and heating the product of such treatment containing the said soluble tin" with about to 50% by weight of sulfur at a temperature sufficiently high to form tin sulfide and for a time sufficient to volatilize the same from the ore undergoing treatment but below that at which the ore fuses;

3. A process for recovering tin in the form of tin sulfide from a low grade tin ore containing about 15% to of tin in a form in which it is' in a substantially aqueous alkali-insoluble state,i

comprisin heating such ore in the presence of about 5% to 40% of a solid carbonaceous reduce ing agent, based on the weight of the ore, at a temperature of at least about 760 C. but below that at which the ore fuses, under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution at a temperature of at least about C. to

C. is produced, and heating the product of such treatment containing the said soluble tin with a sulfidizing agent at a temperature sufliciently high to form tin sulfide and for a time suificient to volatilize the same from the ore un dergoing treatment but below that at which.

the ore fuses.

IRVING E. MUSKAT. ROBERT H. TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,606,343 Burdick Nov. 9, 1926 1,847,991 Sulman et a1. Mar. 1, 1932 FOREIGN PATENTS Number Country Date Great Britain Nov. 27, 1930 

1. A PROCESS FOR RECOVERING TIN IN THE FORM OF TIN SULFIDE FROM A LOW GRADE TIN ORE CONTAINING ABOUT 15% TO 35% OF TIN IN A FORM IN WHICH IT IS IN A SUBSTANTIALLY AQUEOUS ALKALI-INSOLUBLE STATE, COMPRISING HEATING SUCH ORE IN THE PRESENCE OF ABOUT 5% TO 40% OF A SOLID CARBONACEOUS REDUCING AGENT, BASED ON THE WEIGHT OF THE ORE, AT A TEMPERATURE OF AT LEAST ABOUT 760* C. BUT BELOW THAT AT WHICH THE ORE FUSES, UNDER CONDITIONS SUCH THAT REDUCED ORE CONTAINING TIN IN DISPERSED SMALL PARTICLES IN A FORM SOLUBLE IN AQUEOUUS ALKALI SOLUTION AT A TEMPERATURE OF AT LEAST ABOUT 75* C TO 90* C. IS PRODUCED, AND HEATING THE PRODUCT OF SUCH TREATMENT CONTAINING THE SAID SOLUBLE IN WITH A SULFIDIZING AGENT AT A TEMPERATURE OF ABOUT 950* C. TO 1100* C. TO FORM TIN SULFIDE AND FOR A TIME SUFFICIENT TO VOLATILIZE THE SAME FROM THE ORE UNDERGOING TREATMENT. 